Unless otherwise indicated herein, the description in this section is not prior art to the claims in this application and is not admitted to be prior art by inclusion in this section.
There is provided an image forming apparatus such as a Multi-Functional Peripheral (MFP) that can print a document and an image. A color value in a RGB (Red, Green, and Blue) color space is used for general print data of an image forming apparatus. In contrast to this, the color value in a CMYK (Cyan, Magenta, Yellow, black, or Key plate) color space is often used in outputting to recording sheets in the image forming apparatus. In view of this, the image forming apparatus is required to perform a color conversion from the color value in the RGB color space into the color value in the CMYK color space for image formation.
There exist simple conversion equations for the color conversion from the RGB color space into the CMYK color space.C=(1−R−K)/(1−K)M=(1−G−K)/(1−K)Y=(1−B−K)/(1−K)K=min(1−R,1−G,1−B)However, performing the color conversion accurately using the above-described equations is difficult for the model dependent CMYK color space. In view of this, a color conversion table (LUT, Lookup Table) is used for the color conversion from the RGB color space into the CMYK color space. In a color conversion table, when RGB each have 8 bits, holding an assignment of an output value of CMYK or a device independent color space (a CIE XYZ color space, a CIE LAB/CIE LCh color space, or a similar color space) causes to much data volume with respect to input values of about 1678 million colors, which are 256 tones to the third power for each color. In view of this, it is general that the color conversion table, where the data volume is reduced by thinning the colors instead of using all colors in the RGB color space, is created and is stored in the image forming apparatus.
In the color conversion table where the data volume is reduced, the assignment from the color value in the RGB color space into the color value in the CMYK color space is being set for each grid point, which divides the RGB color space at a predetermined interval. For the color value other than the position of the grid point, the color value in the CMYK color space is calculated by an interpolation operation. In the interpolation operation, a method such as a linear interpolation or an interpolation by an approximation formula is used. For example, there is provided an image processing apparatus that preliminarily registers high-order bits as grid point information and low-order bits as information on determining an interpolation proportion and perform an N-point interpolation using information described above.